1. Field of the Invention
The present invention relates to a current reference circuit, and more particularly, to a low temperature coefficient reference current generator.
2. Description of Related Art
In the existing analog circuit design, the analog integrated circuit (IC) usually requires a reference voltage generator and a reference current generator for providing a bias effect, wherein the reference voltage generator can be provided with a low temperature coefficient by using a well-known bandgap technique. However, in order to provide a low temperature coefficient reference current generator, the bandgap reference voltage must be applied to drive a resistor externally connected to the IC. Therefore, the IC must have an additional pin for connecting to the external resistor, which results in a difficulty in miniaturizing the circuit.
To solve such a problem, a direct approach is to fabricate the resistor in the IC. Unfortunately, the resistor that is fabricated by the CMOS (complementary metal oxide semiconductor) IC manufacturing process usually has a relatively large positive temperature coefficient, and thus, the generated current may vary for more than 10% due to the change of the temperature. As a result, the resultant resistor can not meet the requirement of the low temperature coefficient. Therefore, it is desired to have a novel low temperature coefficient reference current generator that is fabricated by standard CMOS IC manufacturing process, while no external resistor is required.
The object of the present invention is to provide a low temperature coefficient reference current generator, which is almost not influenced by the change of the temperature.
To achieve the object, the low temperature coefficient reference current generator in accordance with the present invention includes a bandgap reference voltage generator, a voltage follower and a current mirror circuit. The bandgap reference voltage generator provides a low temperature coefficient bandgap reference voltage and a positive temperature coefficient current. The voltage follower generates a voltage that follows the low temperature coefficient bandgap reference voltage to drive a positive temperature coefficient resistor, so as to produce a negative temperature coefficient current. The current mirror circuit is provided for proportionally amplifying and combining the positive temperature coefficient current and the negative temperature coefficient current, thereby producing a low temperature coefficient reference current.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.